Patent Application
20110070389
The present disclosure relates to a heat-shrinkable coating, in particular, a heat-shrinkable coating with an adhesive. More particularly, the present disclosure relates to a heat-shrinkable coating with an adhesive for covering a metal pipe joint.
Pipes are sold and transported in lengths which may be much shorter than their useful lengths. For example, a given application may require several miles of pipe to be laid, but manufacturing and transporting a pipe with a length of several miles is not practical. Therefore, pipes may be produced in significantly shorter lengths, such as 20, 40 or 80 foot long sections and then assembled together in the field. Metals and/or alloys, such as steel, are routinely used in the manufacture of pipes. During installation, the pipe sections can be welded together at their ends, for example, by butt-welding, to form a single pipe with an extended length.
During the manufacture of pipes, protective coatings may be installed on the surface of the pipe to protect the pipe's metal from oxidation, abrasion, and degradation. Coatings differ vastly based on the application. For example, multilayer polyethylene or polypropylene, fusion bonded epoxy (FBE), enamel, and/or rubber coatings may be used to protect a pipe depending on the environmental conditions to which the pipes will be exposed. During manufacturing, the end portions of a pipe section are left uncoated so that the pipe section can be welded together during installation without interference from or damage to the protective coating. After the pipes are welded, the unprotected end sections and the welded joint may be protected using a sleeve or coating. In combination with the protective coating installed during manufacture, the sleeve allows the protective coating to be continuous over the length of pipe.
A coating in accordance with the present disclosure includes a polyolefin layer and an adhesive layer. In illustrative embodiments, the coating is configured as a sleeve. In another embodiment, the coating is configured as a sheet which can be further configured as a wraparound sleeve during installation.
In illustrative embodiments, the polyolefin layer is heat-shrinkable and woven. In one embodiment, the polyolefin layer includes a polyolefin such as polyethylene, polypropylene, or blends thereof. In one embodiment, the polyolefin is cross-linked. For example, the polyolefin may be irradiatively cross-linked or non-irradiatively cross-linked. In one embodiment the polyolefin is cross-linked by electron-beam irradiation.
In illustrative embodiments, the adhesive layer includes one or more adhesives. For example, adhesives within the scope of the present disclosures include but are not limited to mastics, hot-melts, polyurethanes, polyimides, synthetic rubbers, and epoxies, or blend and combinations thereof. In one embodiment, the pipe coating includes a second adhesive layer. In another embodiment, the second adhesive layer comprises an adhesive distinct from the first adhesive.
In illustrative embodiments, disclosed is an apparatus for covering a pipe including one or more adhesives layers in contact with a heat-shrinkable polyolefin backing, wherein the adhesive layer and the polyolefin backing are arranged to form a composite with a non-continuous dielectric resistance. In one embodiment, the heat-shrinkable polyolefin backing is cross-linked. In another embodiment, the pipe is in contact with the adhesive upon shrinking of the heat shrinkable polyolefin backing and the contact substantially seals the pipe from water and water vapors without sealing the pipe from the passage of current.
An illustrative method of producing a heat shrinkable coating in accordance with the present disclosure comprises the steps of subjecting a woven polyolefin layer to an irradiative cross-linking process, expanding the layer utilizing a stretching device to produce an expanded woven polyolefin layer, and contacting an adhesive layer to the expanded woven polyolefin layer. In one embodiment, the method further comprises the step of contacting the adhesive layer with a release liner. In another embodiment, the method further comprises the step of rolling the film. In yet another embodiment, the method further comprises the step of preheating the woven polyolefin layer. In one embodiment, the method further comprises the step of annealing the expanded woven polyolefin layer. In another embodiment, the method further comprises the step of forming the heat shrinkable coating into a sleeve.
Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived.
The detailed description particularly refers to the accompanying figures in which:
As shown in
Several illustrative pipe-joint coatings are disclosed herein as suggested in
A sleeve 10 in accordance with the present disclosure covers portions of a first pipe unit 111 and a second pipe unit 112. First pipe unit 111 includes a first steel pipe 11 and a first exterior pipe coating 14 as suggested, for example, in
Sleeve 10 is used to cover the exposed portions 11EP, 12EP in a series of illustrative steps shown in
As shown in
As shown in
After sleeve 10 has been heated to shrink and conform to exposed portions 11EP, 12EP of first and second pipes 11, 12, as suggested in
As suggested in
Void spaces 102 may become partially filled with adhesive upon heat shrinking and otherwise may become filled with surrounding materials; therefore, the dielectric resistance of void space 102 is linked to the dielectric resistance of the material which fills void spaces 102. For example, an in-ground pipe application may result in the void spaces 102 being filled with adhesive and with materials characteristic of the application, such as, air, dirt, water, sand, etc. Therefore, the dielectric resistance across the sleeve will be dependent on the dielectric resistance of the void-filling material. In many applications, void spaces 102 will be filled with materials having substantially lower dielectric resistance than polyolefin fibers 101. Accordingly, within an application, sleeve 10 overall will have a dramatically lower dielectric resistance than a comparable sleeve made with a continuous film.
In one aspect, the sleeve 10 exhibits intermittent or non-continuous dielectric resistance, but demonstrates the strength and corrosion protection characteristics of a comparable continuous film. The specifications sufficient to meet the requirements of a given application are strongly influenced by the actual application. For example, a sleeve that may be appropriate to cover the exposed portions of a given pipe may be matched to a particular exterior pipe coating. For example, where the exterior pipe coating includes a multi-layer product comprising of fusion bonded epoxy (FBE) and polyethylene; a sleeve with compatibility towards the FBE, the steel pipe, and the duty requirements of the pipe could be designed. This exemplary exterior pipe coating may be suitable for buried oil and gas pipe in environments where mechanical protection, moisture and corrosion resistance are of primary concern. Thus, a sleeve compatible with this duty would be used in this application. In another example, a pipe being used to transport water at moderate operating temperatures may only require a high density polyethylene extruded over a rubberized mastic adhesive. Accordingly, the sleeve used in this example would be compatible with the high density polyethylene, mastic, and steel. Furthermore, the sleeve's specifications may similarly be aligned to the less demanding duty of this exemplary application.
While the woven polyolefin layer exhibits intermittent or non-continuous dielectric resistance, its properties may be comparable to a cross-linked extruded solid non-woven film with respect to strength and durability. A continuous or monolithic polyolefin film has a high dielectric strength, for example, 100 V/mil or greater is not uncommon. A woven polyolefin backing exhibits non-continuous dielectric resistance due to its non-continuous structure. For example, the interstitial space between the woven polyolefin strands or threads allows for the conduction of current. In one embodiment, the woven polyolefin layer is made from master batches of suitable components including polyolefins, UV stabilizers, colorants, aging stabilizers, and cross-linking additives. During or after extrusion, the polyolefins are cross-linked through a cross-linking treatment. Typically, cross-linking is effectuated through either the inclusion of chemical cross-linking agents or by exposing the woven polyethylene to radiative cross-linking techniques, such as electron beam (e-beam) irradiation.
In illustrative embodiments, a sleeve includes a cross-linked polyolefin layer and an adhesive layer. The cross-linked polyolefin layer is cross-linked so that upon heating, the polyolefin layer shrinks. The cross-linking may be imparted on the polyolefin through irradiation or the incorporation of chemical cross-linking agents. The adhesive includes compatible mastic, hot-melt, epoxy, polyurethane, or other suitable adhesive materials.
In illustrative embodiments, the polyolefin layer is heat shrinkable. In one embodiment, the polyolefin layer shrinks by about 5% to about 200%, based on the reduction in length, upon heating. In another embodiment, the polyolefin layer shrinks by about 10% to about 60%, based on the reduction in length, upon heating. In yet another embodiment, the polyolefin layer shrinks by about 25% to about 50%, based on the reduction in length, upon heating. In one embodiment, the polyolefin layer shrinks from about 10% to about 60%, based on the reduction in length, upon heating. In one embodiment, heating includes raising the temperature of the polyolefin layer to at least about 60 degrees Celsius. In another embodiment, heating includes raising the temperature of the polyolefin layer into a range of about 60 degrees Celsius to about 200 degrees Celsius. In yet another embodiment, heating includes raising the temperature of the polyolefin layer into a range of about 100 degrees Celsius to about 160 degrees Celsius. In one embodiment, the shrink force is greater than about 30 psi, as determined by ASTM D-638 at 150 degrees C. In another embodiment, the shrink force is greater than about 40 psi, as determined by ASTM D-638 at 150 degrees C.
In illustrative embodiments, the polyolefin includes a weave exhibiting a non-continuous dielectric resistance. In one embodiment, the polyolefin exhibits a non-continuous dielectric resistance in the range from about 0 V/mil to about 1000 V/mil, as determined according to ASTM D-149. In another embodiment, the polyolefin exhibits a non-continuous dielectric resistance in the range from about 0 V/mil to about 500 V/mil, as determined according to ASTM D-149. In another embodiment, the polyolefin exhibits a non-continuous dielectric resistance in the range from about 0 V/mil to about 100 V/mil, as determined according to ASTM D-149. In another embodiment, the elongation is greater than or equal to about 300%, as determined by ASTM D-638. In another embodiment, the elongation is greater than or equal to about 500%, as determined by ASTM D-638. In one embodiment, the tensile strength is greater than about 2000 psi, as determined by ASTM D-638. In another embodiment, the tensile strength is greater than about 3000 psi, as determined by ASTM D-638.
The thickness of the woven polyolefin layer and one or more adhesive layers depend on particular application requirements. In one embodiment, the thickness of the woven polyolefin layer is from about 3 to about 50 mils. In another embodiment, the thickness of the woven polyolefin layer is from about 10 to about 30 mils. In yet another embodiment, the thickness of the coating is from about 10 to about 100 mils. In another embodiment, the thickness of the coating is from about 15 to about 80 mils.
In illustrative embodiments, fibers include a cross-linked polyolefin that shrinks upon heating. As used herein, the term polyolefin is used generally to describe a polymer produced from a simple olefin, such as an alkene, with the general formula CnH2n, as a monomer. Polyolefin includes polyethylene and polypropylene and blends thereof. As used herein, the polypropylene (PP) includes polymers with various molecular weights, densities, and tacticities synthesized from propylene monomers.
Polyethylene (PE) includes polymers made through a polymerization of ethylene. For example, PE may include those polymers of ethylene polymerized through a free radical polymerization. For example, PE may have a high degree of short and long chain branching. PE also includes copolymers of ethylene and an alpha olefin comonomer made through a single site catalyzed reaction (e.g., through a metallocene catalyzed reaction) or a blend thereof with an elastomer or high pressure low density polyethylene. PE includes copolymers made with various alpha olefin monomers including 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-hexene, 1-octene or 1-decene. For example, the alpha olefin comonomer may be incorporated from about 1% to about 20% by weight of the total weight of the polymer, preferably from about 1% to about 10° A by weight of the total weight of the polymer. While specific polymer compositions are referred to herein, one of ordinary skill in the art will appreciate that polymers or polymer blends with substantially equivalent physical properties could be substituted, yet remain within the scope and spirit of the present disclosure. In particular, those polymers having substantially equivalent melt indexes (MI) and flow ratios (FR) may be particularly suitable. One of ordinary skill in the art will appreciate that MI (units herein of g/10 min) is an indication of molecular weight, wherein higher MI values typically correspond to low molecular weights. At the same time, MI is a measure of a melted polymer's ability to flow under pressure. FR is used as an indication of the mariner in which rheological behavior is influenced by the molecular weight distribution of the material.
The polyolefin layer is comprised of polyolefin fibers woven into a weave such that the layer exhibits a non-continuous dielectric resistance. As used herein, a fiber is the basic element of a fabric having a length at least 100 times its diameter or width which can be made into a fabric. The term fiber is not limited to a particular geometric cross-section, but instead includes all fiber cross-sections currently known in the art or discovered thereafter. For example, the term fiber includes those fibers having a circular or rectangular cross section. The term fiber includes monofilament fibers or yarns which includes fibers made of two or many filaments. In one embodiment, the weave is selected from a group consisting of plain weave, satin weave, twill weave, basket weave, jacquard weave, rib weave, dobby weave, leno weave, and oxford weave. In another embodiment, the denier of the polyolefin fiber is in the range from about 200 to about 4000 denier. As used herein, the term denier is a unit of measure for the linear mass density of fibers. It is defined as the mass in grams per 9,000 meters of the fiber.
The adhesive may be referred to as an anti-corrosion adhesive because it prevents the penetration of liquids (for example, alkaline or acidic water), gases (for example, air and water vapor), microbes and fungi to the surface of the substrate (for example, pipe). The adhesive is contacted to the woven cross-linked polyolefin layer and forms a layer adjacent to the woven cross-linked polyolefin layer. The coating may be applied to a substrate by arranging the coating so that the adhesive contacts the substrate. The woven cross-linked polyolefin layer is conformable to the shape of the substrate and the adhesive layer provides adhesion between the substrate and the woven polyolefin layer.
As used herein, the term adhesive includes those materials known in the art as adhesives. For example, one of ordinary skill in the art would appreciate that mastic, hot-melt, polyurethane, polyimide, synthetic rubber, and epoxy adhesives may be used. One aspect of the present disclosure is that the adhesive layer assures long-term bonding of the polyolefin layer to the pipe or substrate, and provides principal corrosion resistance and added mechanical strength to the coating.
In one embodiment, at least one adhesive has a softening point of greater than 50 degrees C., as determined by ASTM E-28. In another embodiment, at least one adhesive has a softening point of greater than 80 degrees C., as determined by ASTM E-28. In yet another embodiment, at least one adhesive has a softening point of greater than 100 degrees C., as determined by ASTM E-28. In one embodiment, at least one adhesive has a peel to steel of greater than 10 lbs/in. width, as determined by ASTM D-1000. In another embodiment, at least one adhesive has a peel to steel of greater than 15 lbs/in. width, as determined by ASTM D-1000. In yet another embodiment, at least one adhesive has a peel to steel of greater than 20 lbs/in. width, as determined by ASTM D-1000. In one embodiment, at least one adhesive has an impact resistance of greater than 20 in-lbs, as determined by ASTM G-14. In another embodiment, at least one adhesive has an impact resistance of greater than 30 in-lbs, as determined by ASTM G-14. In yet another embodiment, at least one adhesive has an impact resistance of greater than 40 in-lbs, as determined by ASTM G-14. In one embodiment, at least one adhesive has a penetration resistance of less than about 20%, as determined by ASTM G-17. In another embodiment, at least one adhesive has a penetration resistance of less than about 15%, as determined by ASTM G-17. In yet another embodiment, at least one adhesive has a penetration resistance of less than about 10%, as determined by ASTM G-17.
Surprisingly, it was found that embodiments of the present disclosure were also more conformable than continuous films with similar specifications. Accordingly, embodiments of the present disclosure may be useful in a broader range of potential applications. The use of a woven polyolefin provides improved compatibility between the adhesive layer and polyolefin layer. While not being limited to theory, the compatibility of the adhesive layer and a woven polyolefin layer is improved because the adhesive may inter-digitate the woven layer partially filling the voids. This inter-digitation increases the surface contact area between the adhesive and the polyolefin and may result in additional physical inter-locking which could not occur with a continuous film.
As shown in
